1. Field of the Invention
The present invention relates to a technique for evaluating an interference moiré occurred in a halftone dot image.
2. Description of the Related Art
A proof of a halftone dot image is usually made before the final printing. Proofs are conventionally made with a dedicated proof printer using halftone dots. Recently non-dot hard proof is available where images are printed by means of an inexpensive color printer without using halftone dots, and soft proof is also available where a proof image is displayed on a display device.
FIGS. 8A and 8B depict typical square halftone dots used for printing. The halftone dots have a periodic structure defined by a halftone dot pitch Pd and a screen angle θ. As used herein, the term “halftone dot” will refer to a dot in such a cyclic pattern.
In some cases, a target image to be printed contains cyclic patterns such as striped patterns or meshed patterns. When the target image is printed as a halftone dot image, interference occurs between the pattern cycle within the original target image and the cycle of the halftone dot structure, yielding a pattern that is absent from the original target image. The pattern caused by the interference is referred to as an “interference moiré”.
The aforementioned non-dot hard proofs and soft proofs are advantageous in that they are inexpensive and involve simpler proofing procedures because there is no need to use dedicated proof printers. However, such non-dot hard proofs and soft proofs are still disadvantageous in that an interference moiré cannot be detected because no halftone dots are used.